Dock boards in general are installed on loading docks to bridge or span the gap between the dock and the bed of a truck or other carrier, whereby to provide for convenient loading or unloading of the carrier. The conventional dock board includes a ramp which is pivotably mounted at its rear edge to the loading dock, with the front edge of the ramp being located adjacent to the front of the dock and being provided with an extension flange or lip which is hinged to the ramp. Typically, an entire dock board might be mounted within a shallow pit or depression in the dock and when in the storage position, the ramp will be flush with the upper surface of the dock and the lip will hang downwardly in a pendant position.
To operate a conventional dock board, the truck or other carrier to be loaded or unloaded is backed into position in confronting relationship with the dock and a hold-down device, which normally functions to maintain the ramp in a horizontal position, is manually released, therby permitting some type of spring or counter-balancing means to bias the ramp upwardly to a relatively elevated position. At the same time, the extension lip may be extended to a position somewhat short of its fully extended working position. When the ramp is in this position, the operator can walk out onto the ramp and the weight of the operator overcomes the force of the counter-balancing or spring mechanism, with the result that the ramp is biased downwardly under the weight of the operator and the extension lip is moved down onto the carrier bed. Normally, such dock boards are provided with support legs that extend downwardly from the undersides thereof and are adapted for engagement with a suitable support surface for supporting the ramp in a generally horizontal orientation, with such legs serving to support the ramp entirely or to supplement the associated carrier bed in supporting the ramps in the loading configuration.
One potentially serious problem which exists in connection with dock boards resides in the fact that bodily injury and property damage may very likely occur when the carrier prematurely leaves the loading dock, thus leaving the outer or cantilevered end of the ramp unsupported. Such a problem is particularly serious in the event the carrier prematurely moves at such time as relatively heavy equipment, such as a fork-lift truck or other cargo carrying vehicle happened to be traversing the ramp.
While a large variety of various types of devices have been heretofore provided for assuring against possible bodily and property damage in the event of an occurrence such as that described above, the various devices in the prior art have been objectionable from the standpoint that they have been extremely complicated in structure and operation and therefore are subject to malfunction, as well as being extremely expensive to install, maintain and operate. Additionally, many of the devices heretofore known in the prior art have not been failsafe so that in the event of a malfunction of the support mechanism for the ramp, the ramp itself was subject to suddenly dropping downwardly, resulting in injury or damage to any persons or equipment thereon or in the vicinity thereof.
The present invention is directed toward a novel support assembly adapted to be operatively associated with dock boards of the above described type and which is adapted to overcome the many objectionable characteristics of similar type dock board support arrangements heretofore known and used. In particular, the dock board support assembly of the present invention comprises a piston and cylinder arrangement which is cooperative with a supply of hydraulic operating fluid and which includes a novel valve arrangement whereby the ramp may be biased downwardly under the influence of the weight of the operator or some other predetermined magnitude of loading on the ramp; however, in the event the ramp is subjected to some higher magnitude of loading, the degree of which may be controlled by properly designing the aforesaid valve means, the support assembly positively resists further downward movement of the ramp. Moreover, the higher the pressure or degree of loading of the ramp, the more positive the supporting action of the support assembly, with the result that the assembly is failsafe. In addition, the support assembly of the present invention is completely self-contained and thus requires no auxiliary plumbing, valving or hydraulic pumps or the like and thus may be economically manufactured, maintained and will have a long and effective operational life.